The specificities and numbers of lymphocytes in animals are tightly controlled to avoid autoimmunity and to avoid accumulation of lymphocytesgeneratedduring previous infections. This control can be achieved through the death of autoreactive lymphocytes as consequenceof selection events. Similarly, many lymphocytes that are generated in response to infections die when the infectious agent disappears. The lymphocyte repertoire is also influenced by the ability of lymphocytes to alter their antigen receptor. For example, the antigen receptor expressed by some autoreactive lymphocytes can be modified either by deletion of the genes encoding the offending receptor, or by silencing the action of the autoreactive receptor. At the peak of an immune response against a natural infection, a host can generate pathogen-specific T cell responses that comprise 20-50% of the hosts' total T cell pool. We have now identified a vaccination strategy that is able to generate a similar level of T cell expansion from a purely molecular based vaccine, a result not possible with previously developed vaccine strategies. These high levels of CD8+ T cell expansion can be achieved by the vaccination of a host with antigen in combination with agonists for both the Toll-Like Receptor (TLR) and CD40 pathways (combined TLR/CD40-agonist immunization). We have further identified Type 1 interferon (IFNap) as a central mediator of this synergy in response to certain TLR/CD40- agonist combinations. As IFNap is more often associated with inhibition of virus replication rather than promotion of CD8+ T cell expansion, these studies have identified a potentially novel role for IFNap in promoting adaptive immunity. Most recently, we have observed that both regulatory CD4 cells and dendritic cells expression of TNF ligand superfamily members are critical components by which IFNap influences CD8+ T cell immunity. In the studies proposed here, the mechanism(s) by which IFNap promotes CD8+ T cell expansion and long term protective immunity following combined TLR/CD40-agonist immunization will be determined. Understanding these mechanisms will naturally lead to the development of more potent vaccines against diseases such as HIV, HCV and cancer; diseases whose treatment seems to require the magnitude of cellular immunity that only combined TLR/CD40-agonist immunization is capable of generating.